System and method for operating a compressor

ABSTRACT

A compressor that compresses a fluid during a compression stroke to pressurize the fluid includes an inlet adapted to intake the fluid at an inlet pressure. An inlet valve is coupled to the inlet and adapted to employ a valve closing time during the compression stroke. The compressor further includes an outlet adapted to discharge the fluid subsequent to the compression stroke.

BACKGROUND

The invention relates generally to a reciprocating compressor and, morespecifically, to a system and method for controlling a valve closingtime of a compressor inlet valve.

A compressor is typically used to boost pressure of a working fluid byreceiving power from an electric machine or a turbine, and applying acompressive force to the working fluid. The working fluid may be air,refrigerant, or the like. Compressors are typically classified aspositive displacement compressors, dynamic compressors or turbocompressors, depending on the method they employ for compression.

Positive displacement compressors are typically used to boost pressureof the working fluid by reduction in volume, and may be furtherclassified into categories of reciprocating compressors and rotarycompressors. Reciprocating compressors typically compress the workingfluid via a piston reciprocating inside a cylinder. Rotary compressorstypically compress the working fluid via a roller revolving inside acylinder having an eccentricity.

Large industrial reciprocating compressors are often operated atconstant speed. Such compressors may be operated at partial load bycontrolling opening and closing of compressor inlet valves. By varyingthe timing of the opening and closing of compressor valves, the massflow of fluid through the compressor is reduced. Hence, overallperformance of the compressor over widely varying speed and load rangesmay be improved. Those of ordinary skill in the art will appreciate thatthe phase angle between a crankshaft and a camshaft may be changed so asto adjust the valve timing events. In this way, it is possible to obtainimproved performance for a wider range of engine running characteristicsand conditions than when fixed valve timing is employed.

In one example, the compressors use a hydraulic actuation mechanism tocontrol the opening and closing of the inlet valve during partial loadconditions. The pressure control of the hydraulic actuation mechanism iscontrolled via electromagnetic valves. Thereby, mass flow of fluidthrough the compressor is reduced and the performance of the compressoris enhanced. Such hydraulic actuation mechanisms may employ highpressure pipes and in addition electrical connections to each inletvalve. Moreover, such hydraulic systems do not facilitate flexibility inthe controlled opening and closing of inlet valve during partial loadconditions.

An improved system and method for controlling valve timing of compressorinlet valves to achieve flexibility in partial load operation of thecompressor is desirable.

BRIEF DESCRIPTION

In accordance with one aspect of the present embodiment, a compressorincludes an inlet adapted to intake a fluid at an inlet pressure and aninlet valve coupled to the inlet. The inlet valve is adapted to controlintake of the fluid at the inlet pressure through the inlet. Thecompressor further includes a cam adapted to control a valve closingtime of the inlet valve during a compression stroke of the compressor topressurize the fluid. Also included is an outlet adapted to dischargepressurized fluid subsequent to the compression stroke.

In accordance with another aspect of the present embodiment, acompressor includes an inlet adapted to intake a fluid at an inletpressure and an inlet valve coupled to the inlet. The inlet valve isadapted to control intake of the fluid at the inlet pressure through theinlet. The compressor further includes at least one blocking solenoidadapted to control a valve closing time of the inlet valve during acompression stroke of the compressor, the at least one blocking solenoidbeing further adapted to maintain the inlet valve at least one stoppoint during the compression stroke of the compressor.

In accordance with another aspect of the present embodiment, a method ofoperating a compressor includes supplying a fluid at the inlet pressurevia an inlet. The method further includes actuating a cam to control avalve closing time of an inlet valve coupled to the inlet during thecompression stroke of the compressor.

In accordance with another aspect of the present embodiment, a method ofoperating a compressor includes supplying a fluid at an inlet pressurevia an inlet; and actuating at least one blocking solenoid to controlvalve closing time of an inlet valve coupled to the inlet during acompression stroke of the compressor.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical representation of a reciprocating compressorhaving valve closing control features in accordance with an exemplaryaspect of the present embodiment;

FIG. 2 is a detailed diagrammatical representation of a reciprocatingcompressor having valve closing control features in accordance with anexemplary aspect of the present embodiment;

FIG. 3 is a diagrammatical representation of a reciprocating compressorhaving a cam adapted to control valve closing time of an inlet valve inaccordance with an exemplary aspect of the present embodiment;

FIG. 4 is a graph representing variation of pressure versus volumeduring a full load cycle operation of a reciprocating compressor inaccordance with an exemplary aspect of the present embodiment;

FIG. 5 is a graph representing variation of pressure versus volumeduring a partial load cycle operation of a reciprocating compressor inaccordance with an exemplary aspect of the present embodiment;

FIG. 6 is a diagrammatical representation of a reciprocating compressorhaving a plurality of blocking solenoids adapted to control valveclosing time of an inlet valve in accordance with an exemplary aspect ofthe present embodiment; and

FIGS. 7 and 8 are flow charts illustrating exemplary processes ofoperating a compressor in accordance with certain exemplary aspects ofthe present embodiment.

DETAILED DESCRIPTION

Referring generally to FIG. 1, in accordance with several aspects of thepresent embodiment, a compressor 10 includes a piston 38 slidablyinserted inside a cylinder 42. A suction valve assembly 46 is providedfor opening and closing a suction hole 11 mounted at a front side of thepiston 38. The suction valve assembly is adapted to control intake offluid through the suction hole 11. The compressor 10 further includes anelectromechanical valve mechanism 52 adapted to control a valve closingtime of an inlet valve (not shown) during a compression stroke of thecompressor 10 to pressurize the fluid. A control unit 54 may be coupledto the electro-mechanical valve actuation mechanism 52 and configured tocontrol the operation of the valve actuation mechanism 52.

Referring now to FIG. 2, this figure additionally shows further optionalexemplary aspects for compressor 10 which are described in greaterdetail. The reciprocating compressor 10 may be used for domestic andindustrial purposes. The compressor 10 is typically driven by anelectric motor, steam or gas turbine, combustion engine, or the like. Asappreciated by those of ordinary skill in the art, the compressor 10 maybe used to compress air, hydrogen, methane, butane, or other liquids orgases. The reciprocating compressor 10 includes a suction pipe or inlet12 and a discharge pipe or outlet 14 coupled to a casing 16. The suctionpipe 12 is configured to receive a fluid at an inlet pressure and thedischarge pipe 14 is configured to discharge a compressed fluid. Theinlet pressure of the fluid may be ambient pressure or any otherappropriate pressure as known to those skilled in the art. Areciprocating motor 18 is disposed inside the casing 16 for generating areciprocation force. A compressing unit 20 is also located inside thecasing 16 and configured to compress the fluid by receiving thereciprocation force generated from the reciprocating motor 18. Aplurality of frames 22, 24, and 26 are provided for supporting thereciprocating motor 18 and the compressing unit 20.

The reciprocating motor 18 includes an outer stator 28 having acylindrical shape and an inner stator 30 disposed along an innercircumferential surface of the outer stator 28. A coil 32 is woundwithin the outer stator 28. A magnet 34 is reciprocatably disposed inthe air gap between the outer stator 28 and the inner stator 30. Themagnet 34 is fixed to an outer circumferential surface of a magnetholder 36. The magnet holder 36 is coupled to the piston 38 of thereciprocating compressor 10.

A first resonant spring 39 is disposed between one side surface of themagnet holder 36 and the frame 22 and a second resonant spring 40 isdisposed between another side surface of the magnet holder 36 and theframe 24, to induce a resonant movement of the piston 38. The piston 38is slidably inserted inside the cylinder 42 forming a compressionchamber 44. The suction valve assembly 46 is provided for opening andclosing a suction hole mounted at a front side of the piston 38. Adischarge valve assembly 48 is mounted at a front side of the cylinder42 for discharging the compressed fluid when a pressure inside thecompression chamber 44 is greater than a preset pressure. A fluidsuction passage 50 is formed along a longitudinal direction in thepiston 38.

When the reciprocating motor 18 is operated, the magnet 34 is linearlyreciprocated and thereby the piston 38 coupled to the magnet is linearlyreciprocated to compress the fluid. When the piston 38 is retreated, theinlet valve of the suction valve assembly 46 is opened by a differentialpressure between the fluid introduced into the suction passage 50 of thepiston 38 and the compression chamber 44 of the cylinder 42. When thepiston 38 is advanced, the inlet valve is closed and thereby fluidinside the compression chamber 44 is compressed. Also, when a pressureinside the compression chamber 44 is greater than a predeterminedpressure, a discharge valve (not shown) of the discharge valve assembly48 is opened and thereby the compressed fluid is discharged through thedischarge pipe 14.

As noted above, during compression stroke, the inlet valve is closed dueto differential pressure between the fluid introduced into the suctionpassage 50 of the piston 38 and the compression chamber 44 of thecylinder 42. In the illustrated embodiment, the electro-mechanical valveactuation mechanism 52 is employed to control the closing of the inletvalve during the compression stroke of the compressor 10 at no-load orpartial load operating conditions. In order to achieve flexibilityduring no-load or partial load operation of the compressor 10, theelectro-mechanical valve actuation mechanism 52 enables to control theclosing time of the inlet valve during the compression strokeindependent of crank motion of the compressor 10. Various exemplaryembodiments of the electro-mechanical valve actuation mechanism 52 areexplained in greater detail with respect to subsequent figures. Thecontrol unit 54 may be coupled to the electro-mechanical valve actuationmechanism 52 and configured to control the operation of the valveactuation mechanism 52. In one embodiment, the control unit 54 includesan electronic logic controller that is programmable by a user. Thecontrol unit 54 may control the valve actuation mechanism 52 based onthe load condition of the compressor. Those of ordinary skill in the artwill appreciate in light of the present discussion that any number ofcompressor constructions are envisaged.

Referring generally to FIG. 3, one embodiment of the electro-mechanicalvalve actuation mechanism 52 is illustrated. The electromechanical valveactuation mechanism 52 includes a cam 68 adapted to be electricallydriven by a rotary drive unit 70 such as an electrical motor or arotational solenoid. The cam 68 may be stopped and held in any arbitraryposition within the predetermined limits to control the closing of theinlet valve 55 during the compression stroke. FIG. 3 additionally showsfurther optional exemplary aspects for electromechanical valve actuationmechanism 52 which are described in more detail below.

The inlet valve 55 of the suction valve assembly 46 is provided foropening and closing the suction hole mounted at the front side of thepiston. The inlet valve 55 includes a valve plate 56, two plates (58,60) mutually coupled via a plurality of springs 62. The plurality ofsprings 62 is provided to bias the plate 58 against the valve plate 56.The valve plate 56 includes a plurality of holes 64 and inlet openings66. In the illustrated embodiment, the electromechanical valve actuationmechanism 52 includes the cam 68 adapted to be electrically driven bythe rotary drive unit 70 such as an electrical motor or a rotationalsolenoid. The drive unit 70 is operable at constant speed or variablespeed. The rotary drive unit 70 may be rotated 90 degrees in ananticlockwise direction to close the inlet valve 55. In certain otherembodiments, the rotary drive unit 70 may be rotated 90 degrees in aclockwise direction to close the inlet valve 55. The cam 68 drives apushing rod (unloader) 72 adapted to follow the motion of the inletvalve 55 and hold the inlet valve 55 at an open position. The pushingrod 72 includes two plate portions (76, 79), a rod portion 74 extendingbetween the plate portions (76, 79), and a plurality of projections 78extending from the plate portion 76. When the pushing rod 72 is drivenby the cam 68, the projections 78 penetrate through the holes 64 formedin the valve plate 56 to disengage the plate 58 from the valve plate 56.Fluid is then sucked through the inlet openings of the valve plate 56.

Although in the illustrated embodiment, one inlet valve 55 is shown, thecompressor may include a plurality of inlet valves 55 adapted to controlthe intake of fluid into the compressor 10. The electro-mechanical valveactuation mechanism 52 may include one cam and one drive unit per valve,in order to operate each valve separately and ensure flexibility. Forexample, depending on the load condition of the compressor, it may berequired to vary the closing time of one set of valves from the closingtime of the other set valves during compression stroke of thecompressor. The cam 68 is adapted to hold the valve 55 in the openposition without the requirement of any external force or energy. Thecam 68 may be stopped and held in any arbitrary position within thepredetermined limits to control the closing of the inlet valve 55 duringthe compression stroke.

In the illustrated embodiment, the inlet valve 55 is operable in twomodes. During no-load condition or partial load condition, a peakportion 80 of the cam 68 contacts the pushing rod 72 and the inlet valve55 is fully opened. During full load condition, the cam 68 is disengagedfrom the pushing rod 72 and the inlet valve 55 is in free floatingcondition, enabling the inlet valve 55 to be opened and closed due todifferential pressure.

In the illustrated embodiment, the control unit 54 may further include adatabase 82, an algorithm 84, and a data analysis block 86. The database82 may be configured to store predefined information about thecompressor 10. For example, the database 82 may store informationrelating to crank angle, compressor speed, compressor load, intake fluidpressure, compressed fluid pressure, type of fluid, or the like. Thedatabase 82 may also include instruction sets, maps, lookup tables,variables, or the like. Such maps, lookup tables, instruction sets, areoperative to correlate characteristics of the valve closing time tospecified compressor operation parameters such as compressor speed,crank angle, compressor pressure, compressor load, type of fluid, or thelike. Furthermore, the database 82 may be configured to store actualsensed/detected information pertaining to the compressor 10. Thealgorithm 84 may facilitate the processing of sensed informationpertaining to the compressor 10.

The data analysis block 86 may include a variety of circuitry types,such as a microprocessor, a programmable logic controller, a logicmodule or the like. The data analysis block 86 in combination with thealgorithm 84 may be used to perform the various computational operationsrelating to determination of closing time of the inlet valves 55,predetermined time period for controlling closing time of the inletvalves 55, degree of rotation of the rotary drive unit 70, powerrequired to drive the valve actuation mechanism 52, or a combinationthereof. Any of the above mentioned parameters may be selectively and/ordynamically adapted or altered relative to time.

Referring to FIG. 4, a graph representing variation of cylinder pressureversus cylinder volume during a full load cycle operation of thereciprocating compressor is illustrated. Dashed lines 61, 63 representstop dead center position and bottom dead center position respectively ofthe piston. Operating point 65 represents piston positioned at the topdead center and the discharge valve held in closed position. Duringintake stroke, the piston is moved to the bottom dead center and isrepresented by the curve 67. Pressure is reduced and the volume isincreased in the cylinder during intake stroke. Operating point 69represents opening of the inlet valve during intake stroke of the pistonand supply of fluid into the cylinder. The inlet valve is opened by adifferential pressure between the fluid introduced into the suctionpassage of the piston and the compression chamber of the cylinder. Whenthe piston reaches the bottom dead center position, the inlet valve isclosed as represented by the operating point 71.

During compression stroke, the piston is moved from the bottom deadcenter to the top dead center and is represented by the curve 73. Fluidinside the cylinder is compressed. Therefore, pressure is increased andthe volume is reduced in the cylinder during compression stroke.Operating point 75 represents opening of the discharge valve duringcompression stroke of the piston and discharge of compressed fluid. Whenthe piston reaches the top dead center position, the discharge valve isclosed. The cycle is repeated. In the illustrated embodiment, the inletvalve is in free-floating condition during full load operation. As aresult, the compressor delivers 100% mass flow through the cylinder.

Referring to FIG. 5, a graph representing variation of cylinder pressureversus cylinder volume during a partial load cycle operation of thereciprocating compressor is illustrated. As described above, dashedlines 61, 63 represent top dead center position and bottom dead centerposition respectively of the piston. Operating point 65 representspiston positioned at the top dead center and the discharge valve held inclosed position. During intake stroke, the piston is moved to the bottomdead center and is represented by the curve 67. Pressure is reduced andthe volume is increased in the cylinder during intake stroke. Operatingpoint 69 represents opening of the inlet valve during intake stroke ofthe piston and supply of fluid into the cylinder. The inlet valve ismaintained in free-floating condition during intake stroke.

When the piston reaches the bottom dead center position, the inlet valveis further maintained in the open position using the electro-mechanicalvalve actuation mechanism as described previously. During compressionstroke, the piston is moved from the bottom dead center to the top deadcenter and is represented by the curve 73. Fluid inside the cylinder iscompressed. Therefore, pressure is increased and the volume is reducedin the cylinder during compression stroke. Since the inlet valve ismaintained open for a predetermined period during compression stroke,reverse fluid flow may occur through the inlet of the compressor.Operating point 77 represents closing of the inlet valve during thecompressor stroke of the piston. The electro-mechanical valve actuationmechanism is released to close the inlet valve. In the illustratedembodiment, the closing of the inlet valve is delayed using theelectro-mechanical valve actuation mechanism. Operating point 75represents opening of the discharge valve during compression stroke ofthe piston and discharge of compressed fluid. When the piston reachesthe top dead center position, the discharge valve is closed. In theillustrated embodiment, mass flow through the compressor is reducedduring partial load condition. For example, during 50% load condition ofthe compressor, 50% of mass flow is delivered through the compressor.The usage of electro-mechanical mechanism further facilitates to reducepower consumption for maintaining the inlet valve open duringcompression stroke.

Referring generally to FIG. 6, another embodiment of theelectro-mechanical valve actuation mechanism 52 is illustrated. In theillustrated embodiment, the electromechanical valve actuation mechanism52 includes a plurality of blocking solenoids (88, 90) adapted to beactuated by the control unit 54. The blocking solenoid 88 maintains theinlet valve in an open position for a predetermined time period duringcompression stroke. FIG. 6 additionally shows further optional exemplaryaspects for electromechanical valve actuation mechanism 52 which aredescribed in more detail below.

A drive unit 92, such as a spring or a pusher solenoid, drives thepushing rod (unloader) 72 adapted to follow the motion of the inletvalve 55 and hold the inlet valve 55 at an open position. As discussedabove with respect to FIG. 3, when the pushing rod 72 is driven by thedrive unit 92, the projections 78 penetrate through the holes 64 formedin the valve plate 56 to disengage the plate 58 from the valve plate 56and fluid is sucked through the inlet openings of the valve plate 56.

During an intake stroke, the inlet valve is opened due to thedifferential pressure between the fluid introduced into the suctionpassage 50 of the piston 38 and the compression chamber 44 of thecylinder 42. In one example, during no-load or partial load condition,the control unit 54 electrically actuates the blocking solenoid 88adapted to drive a blocking rod 98 so that the blocking rod 98 engages abore 100 formed in the pushing rod 72. The blocking solenoid 88 isconfigured to hold the pushing rod 72 at a first stop-point position102. In this manner, the blocking solenoid 88 maintains the inlet valvein an open position for a predetermined time period during compressionstroke. The blocking rod 98 is disengaged from the bore 100 of thepushing rod 72 by releasing the current supplied to the blockingsolenoid 88. The pushing rod 72 and the pusher solenoid 92 are actuatedin an opposite direction relative to the intake stroke, due to thedifferential pressure causing the inlet valve to close.

In another example, during no-load or partial load condition, thecontrol unit 54 electrically actuates the blocking solenoid 90 adaptedto drive a blocking rod 104 so that the blocking rod 104 engages a bore106 formed in the pushing rod 72. The blocking solenoid 90 is configuredto hold the pushing rod 72 at a second stop-point position 108. In thismanner, the blocking solenoid 90 maintains the inlet valve in an openposition for a predetermined time period during compression stroke. Theblocking rod 104 is disengaged from the bore 106 of the pushing rod 72by releasing the current supplied to the blocking solenoid 90. Thepushing rod 72 and the pusher solenoid 92 are actuated in an oppositedirections relative to the intake stroke, due to the differentialpressure causing the inlet valve to close. Although in the illustratedembodiment, two blocking solenoids are illustrated, the valve actuationmechanism 52 may include multiple blocking solenoids configured to holdthe pushing rod 72 at a plurality of stop points during the compressionstroke. One type of blocking solenoid may be used for variety ofcompressor applications.

FIG. 7 is a flow chart illustrating a method of operating the compressor10 in accordance with an exemplary embodiment of the present embodiment.The method includes sucking fluid via the suction pipe 12 during intakestroke as represented by step 110. During no-load or partial loadoperation of the compressor 10, the electromechanical valve actuationmechanism 52 enables to control the closing time of the inlet valve 55during the compression stroke independent of the crank motion of thecompressor 10.

Operation of the rotary drive unit 70 such as the electrical motor orrotational solenoid is controlled via the control unit 54 based on theload condition of the compressor as represented by step 112. The cam 68is driven by the rotary drive unit 70 as represented by step 114. Thecam 68 drives the pushing rod 72 in such a way that the plurality ofprojections 78 of the pushing rod 72 penetrate through the holes 64formed in the valve plate 56 as represented by step 116. The fluid issucked through the inlet openings 66 formed in the valve plate 56. Theinlet valve 55 is opened due to differential pressure between the fluidintroduced at inlet pressure into the suction passage of the piston 38and compression chamber 44 of the cylinder 42. The cam 68 is stopped inthe predetermined position to control the closing time of the valve 55during compression stroke of the compressor 10 as represented by step118. During no-load condition, the peak portion of the cam 68 is engagedwith the pushing rod 72 to hold the inlet valve in the fully openposition.

During compression stroke, the cam 68 is further actuated by the driveunit 70 to release the cam 68 from the pushing rod 72 such that theinlet valve 55 is closed due to differential pressure acting in anopposite relative to the intake stroke. Thereby fluid inside thecompression chamber 44 of the cylinder 42 is compressed. The compressedfluid is discharged via the discharge pipe 14 as represented by step120.

Referring to FIG. 8, this figure illustrates another embodiment of themethod of operating the compressor 10 in accordance with an exemplaryembodiment of the present embodiment. The method includes sucking fluidvia the suction pipe 12 during intake stroke as represented by step 122.As noted in the previous embodiment, during no-load or partial loadoperation of the compressor 10, the electromechanical valve actuationmechanism 52 enables to control the closing time of the inlet valve 55during the compression stroke independent of the crank motion of thecompressor.

The drive unit 92 such as the spring or the pusher solenoid drives thepushing rod 72 (unloader) as represented by step 124. The pushing rod 72follows the motion of the inlet valve 55 and facilitates to hold theinlet valve 55 at an open position. The projections 78 of the pushingrod 72 penetrates through the holes 64 formed in the valve plate 56 toenable suction of fluid through the inlet openings 66 formed in thevalve plate 56. During no-load or partial load conditions, the controlunit 54 actuates the blocking solenoid as represented by step 126. Theblocking solenoid actuates the blocking rod as represented by step 128.The blocking rod engages a bore formed in the pushing rod 72 at a stoppoint as represented by step 130. The blocking solenoid facilitates tohold the inlet valve 55 at the open position for a predetermined timeperiod during the compression stroke, thereby enabling to control thevalve closing time of the inlet valve 55 during the compression strokeas represented by step 132.

As discussed above, during compression stroke, the blocking solenoid isfurther actuated by the drive unit 92 to release the blocking rod fromthe pushing rod 72 such that the inlet valve 55 is closed due todifferential pressure acting in an opposite relative to the intakestroke. Thereby fluid inside the compression chamber 44 of the cylinder42 is compressed. The compressed fluid is discharged via the dischargepipe 14 as represented by step 134.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A compressor, comprising: an inlet adapted to intake a fluid at aninlet pressure; an inlet valve coupled to the inlet and adapted tocontrol intake of the fluid at the inlet pressure through the inlet; acam adapted to control a valve closing time of the inlet valve during acompression stroke of the compressor to pressurize the fluid; and anoutlet adapted to discharge pressurized fluid subsequent to thecompression stroke.
 2. The compressor of claim 1, further comprising anelectric motor adapted to drive the cam.
 3. The compressor of claim 1,further comprising a rotational solenoid adapted to drive the cam. 4.The compressor of claim 3, wherein the rotational solenoid is rotated 90degrees in an anticlockwise direction to hold the inlet valve at aclosed position.
 5. The compressor of claim 3, wherein the rotationalsolenoid is rotated 90 degrees in a clockwise direction to hold theinlet valve at a closed position.
 6. The compressor of claim 1, furthercomprising an unloader adapted to be driven by the cam to control thevalve closing time of the inlet valve for a predetermined time periodduring the compression stroke of the compressor.
 7. A compressor,comprising: an inlet adapted to intake a fluid at an inlet pressure; aninlet valve coupled to the inlet and adapted to control intake of thefluid at the inlet pressure through the inlet; and at least one blockingsolenoid adapted to control a valve closing time of the inlet valveduring a compression stroke of the compressor, the at least one blockingsolenoid being further adapted to maintain the inlet valve at least onestop point during the compression stroke of the compressor.
 8. Thecompressor of claim 7, further comprising an unloader adapted to bedriven by a pusher solenoid.
 9. The compressor of claim 8, furthercomprising at least one blocking rod adapted to hold the unloader atleast one stop point during the compression stroke of the compressor.10. The compressor of claim 9, wherein the blocking rod is actuated bythe blocking solenoid.
 11. A method of operating a compressor,comprising: supplying a fluid at an inlet pressure via an inlet; andactuating a cam to control valve closing time of an inlet valve coupledto the inlet during the compression stroke of the compressor.
 12. Themethod of claim 11, further comprising actuating an electric motor todrive the cam.
 13. The method of claim 11, further comprising actuatinga rotational solenoid to drive the cam.
 14. The method of claim 13,comprising rotating the solenoid 90 degrees along an anticlockwisedirection to hold the inlet valve at a closed position.
 15. The methodof claim 13, comprising rotating the solenoid 90 degrees along aclockwise direction to hold the inlet valve at a closed position. 16.The method of claim 11, further comprising actuating an unloader bydriving the cam.
 17. A method of operating a compressor, comprising:supplying a fluid at an inlet pressure via an inlet; and actuating atleast one blocking solenoid to control valve closing time of an inletvalve coupled to the inlet during a compression stroke of thecompressor.
 18. The method of claim 17, comprising actuating theblocking solenoid to maintain the inlet valve at least one stop pointduring compression stroke of the compressor.
 19. The method of claim 17,comprising actuating an unloader to control valve closing time of theinlet valve.
 20. The method of claim 19, further comprising actuating apusher solenoid to drive the unloader.
 21. The method of claim 19,comprising actuating at least one blocking rod via the blocking solenoidto hold the unloader at least one stop point during the compressionstroke of the compressor.